Share-Based Payment Arrangements, Allocation of Recognized Period Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expense recognized	$ 2,948	$ 3,523	$ 3,546
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expense recognized	1,099	1,843	2,012
General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total compensation expense recognized	$ 1,849	$ 1,680	$ 1,534